High aluminum containing manganese steel and methods of preparing and using the same

ABSTRACT

Described herein are high aluminum containing manganese steels and methods of preparing and using the same. In some embodiments, the steel of the present invention is in the form of a steel plate and may be suitable for thick plate structural applications. A steel of the present invention comprises manganese, aluminum, carbon, and iron, and one or more of: molybdenum, vanadium, niobium, calcium, silicon, cerium, lanthanum, nickel, chromium, cobalt, and tungsten.

GOVERNMENT SUPPORT

This invention was made with government support under Grant No. W15QKN-14-9-1001 awarded by awarded by the Department of Defense Ordnance Technology Consortium. The U.S. Government has certain rights in the invention.

FIELD

The present invention concerns a high aluminum containing manganese steel and method of preparing and using the same. In some embodiments, the steel of the present invention is in the form of a steel plate and may be suitable for thick plate structural applications.

BACKGROUND

Iron-manganese-aluminum-carbon (Fe—Mn—Al—C) steel alloys have been previously studied for their potential as an alternative steel alloy for Rolled Homogeneous Armor (RHA). Prior tested materials were both wrought and cast versions, but were all less than an inch in thickness. Current carbon steels have not been able to meet the automotive requirements for reduced weight and have driven materials developers to other, sometimes exotic, materials.

SUMMARY

A first aspect of the present invention is directed to a steel comprising aluminum and manganese, iron, and carbon. In some embodiments, the steel comprises, by weight percent: manganese in an amount in a range of about 15% to about 35%, aluminum in an amount in a range of about 7% to about 12%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium or niobium in an amount in a range of about 0.01% to about 2%, calcium in an amount in a range of about 0.01% to about 0.1%, silicon in an amount in a range of about 0.01% to about 1.5%, and a balance comprising iron. In some embodiments, if present, phosphorus is present in an amount less than about 0.0075% by weight percent, sulfur in an amount of less than about 0.01%, and/or nitrogen in an amount of less than about 0.01%.

Another aspect of the present invention is directed to a method for manufacturing a steel plate comprising: casting an alloy to form a preform, the alloy comprising, by weight percent, manganese in an amount in a range of about 15% to about 35%, aluminum in an amount in a range of about 7 to about 12%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium or niobium in an amount in a range of about 0.01% to about 2%, calcium in an amount in a range of about 0.01% to about 0.1%, silicon in an amount in a range of about 0.01% to about 1.5%, and a balance comprising iron; heating the preform to a temperature in a range of about 1000° C. to about 1200° C.; and rolling the preform to form a steel plate. The preform may be an ingot or a slab.

A further aspect is directed to use of a steel as described herein, such as, for example, in ground systems.

It is noted that aspects of the present invention described with respect to one embodiment, may be incorporated in a different embodiment although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. Applicant reserves the right to change any originally filed claim and/or file any new claim accordingly, including the right to be able to amend any originally flied claim to depend from and/or incorporate any feature of any other claim or claims although not originally claimed in that manner. These and other objects and/or aspects of the present invention are explained in detail in the specification set forth below. Further features, advantages and details of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the preferred embodiments that follow, such description being merely illustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image of a strike face of a steel plate according to example embodiments of the present invention upon ballistic testing using .50 caliber APM2 test munition.

FIG. 2 is an image of the back face of the steel plate of FIG. 1.

FIG. 3 is an image of a strike face of a steel plate according to example embodiments of the present invention upon ballistic testing using 20 mm fragmentation simulation projectile (FSP) test munition.

FIG. 4 is an image of the back face of the steel plate of FIG. 3.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention is now described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present application and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of a conflict in terminology, the present specification is controlling.

Also as used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

Unless the context indicates otherwise, it is specifically intended that the various features of the invention described herein can be used in any combination. Moreover, the present invention also contemplates that in some embodiments of the invention, any feature or combination of features set forth herein can be excluded or omitted. To illustrate, if the specification states that a complex comprises components A, B and C, it is specifically intended that any of A, B or C, or a combination thereof, can be omitted and disclaimed.

As used herein, the transitional phrase “consisting essentially of” (and grammatical variants) is to be interpreted as encompassing the recited materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention. See, In re Herz, 537 F.2d 549, 551-52, 190 U.S.P.Q. 461, 463 (CCPA 1976) (emphasis in the original); see also MPEP § 2111.03. Thus, the term “consisting essentially of” as used herein should not be interpreted as equivalent to “comprising.”

The term “about,” as used herein when referring to a measurable value such as an amount or concentration and the like, is meant to encompass variations of ±10%, ±5%, ±1%, ±0.5%, or even ±0.1% of the specified value as well as the specified value. For example, “about X” where X is the measurable value, is meant to include X as well as variations of ±10%, ±5%, ±1%, ±0.5%, or even ±0.1% of X. A range provided herein for a measurable value may include any other range and/or individual value therein.

As used herein, the terms “increase,” “increases,” “increased,” “increasing,” “improve,” “enhance,” and similar terms indicate an elevation in the specified parameter of at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 150%, 200%, 300%, 400%, 500% or more.

As used herein, the terms “reduce,” “reduces,” “reduced,” “reduction,” “inhibit,” and similar terms refer to a decrease in the specified parameter of at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 8, 80%, 85%, 90%, 95%, 97%, or 100%.

Provided herein is a steel comprising manganese, aluminum, carbon, and iron. In some embodiments, the steel comprises manganese, aluminum, carbon, molybdenum, vanadium, niobium, calcium, silicon, and/or iron. In some embodiments, the steel comprises, by weight percent: manganese in an amount in a range of about 15% to about 35%, aluminum in an amount in a range of about 7% to about 12%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium and/or niobium in an amount in a range of about 0.01% to about 2%, calcium in an amount in a range of about 0.01% to about 0.1%, silicon in an amount in a range of about 0.01% to about 1.5%, and a balance comprising iron.

In some embodiments, the steel comprises vanadium and not niobium, or the steel comprises niobium and not vanadium. In some embodiments, the steel comprises vanadium and niobium. Vanadium and/or niobium may be used to increase strength, such as, for example, in a thick section of the steel and/or in the heat affected zone of any welded section.

The steel may also comprise one or more of cerium, lanthanum, nickel, chromium, tungsten, and cobalt, one or more of which may aid in increasing the strength of the steel. In some embodiments, the steel may comprise, by weight percent, cerium in an amount up to about 0.05%, lanthanum in an amount up to about 0.05%, nickel in an amount up to about 5%, chromium in an amount up to about 5%, tungsten in an amount up to about 5%, and/or cobalt in an amount up to about 5%.

Manganese may be present in the steel in an amount by weight percent of about 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%. In some embodiments, manganese is present in the steel in an amount by weight percent in a range of about 28% to about 35%. In some embodiments, manganese is present in the steel in an amount by weight percent in a range of about 15% to about 28% or 29%.

Aluminum may be present in the steel in an amount by weight percent of about 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%. In some embodiments, aluminum is present in the steel in an amount by weight percent of greater than 7%. In some embodiments, aluminum is present in the steel in an amount by weight percent of about 7% or 8%. In some embodiments, aluminum is present in the steel in an amount by weight percent in a range of about 7% to about 10% or 12%.

Carbon may be present in the steel in an amount by weight percent of about 0.7%, 0.8%, 0.9%, 1%, or 1.1%.

Molybdenum may be present in the steel in an amount by weight percent of about 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%.

Vanadium may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6% 17%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. In some embodiments, vanadium is present in the steel in an amount by weight percent in a range of about 0.1% to about 1%.

Niobium may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, In some embodiments, niobium is present in the steel in an amount by weight percent in a range of about 0.1% to about 1%.

Calcium may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%. In some embodiments, calcium may be used and/or is suitable for increasing the strength of the steel and/or reducing or removing phosphorus in the steel.

Silicon may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%.

Cerium may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%. In some embodiments, cerium is not present in the steel or is present in trace amounts.

Lanthanum may be present in the steel in an amount by weight percent of about 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%. In some embodiments, lanthanum is not present in the steel or is present in trace amounts.

Nickel may be present in the steel in an amount by weight percent of about 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In some embodiments, nickel is not present in the steel or is present in trace amounts.

Chromium may be present in the steel in an amount by weight percent of about 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In some embodiments, chromium is not present in the steel or is present in trace amounts.

Cobalt may be present in the steel in an amount by weight percent of about 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In some embodiments, cobalt is not present in the steel or is present in trace amounts.

Tungsten may be present in the steel in an amount by weight percent of about 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In some embodiments, tungsten is not present in the steel or is present in trace amounts.

Iron makes up the balance of the steel to total 100% by weight of the steel. In some embodiments, iron is present in the steel in an amount by weight percent of about 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%.

One or more impurities may be present in the steel, such as, for example, phosphorous, nitrogen, and/or sulfur. If present in the steel, phosphorus may be present in the steel by weight percent in an amount of less than about 0.0075% 0.006%, 0.005%, 0.004%, 0.003%, or 0.002%. If present in the steel, nitrogen and/or sulfur may be present in the steel by weight percent in an amount of less than about 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, or 0.005%.

In some embodiments, a steel of the present invention comprises, by weight percent: manganese in an amount in a range of about 15% to about 28%, aluminum in an amount in a range of about 7% to about 8%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium and/or niobium in an amount in a range of about 0.01% to about 2%, silicon in an amount in a range of about 0.01% to about 1.5%, and a balance comprising iron, wherein phosphorus, if present, is in an amount less than about 0.0075%. The steel may have a composition, by weight percent of: a balance comprising iron, manganese in an amount of 28%, aluminum in an amount of 8%, silicon in an amount of 1%, carbon in an amount of 0.9%, molybdenum in an amount of 0.55%, and vanadium in an amount of 0.55% (i.e., Fe-28Mn-8Al-1Si-0.9C-0.55Mo-0.55V).

In some embodiments, a steel of the present invention comprises, by weight percent: manganese in an amount in a range of about 15% to about 28%, aluminum in an amount in a range of about 7% to about 10%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium and/or niobium in an amount in a range of about 0.01% to about 2%, silicon in an amount in a range of about 0.01% to about 1.5%, nickel in an amount in a range of about 0.01% to about 5%, and a balance comprising iron, wherein phosphorus, if present, is in an amount less than about 0.0075%. The steel may have a composition, by weight percent of: a balance comprising iron, manganese in an amount of 20%, nickel in an amount of 5%, aluminum in an amount of 10%, silicon in an amount of 1%, carbon in an amount of 0.8%, molybdenum in an amount of 0.5%, and vanadium in an amount of 0.5% (i.e., Fe-20Mn-5Ni-10Al-1Si-0.8C-0.5Mo-0.5V).

In some embodiments, a steel of the present invention comprises, by weight percent: manganese in an amount in a range of about 15% about 15% to about 20%, aluminum in an amount in a range of about 7% to about 12%, nickel in an amount in a range of about 0% to about 5%, chromium in an amount in a range of about 0% to about 5%, cobalt in an amount in a range of about 0% to about 5%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium and/or niobium in an amount in a range of about 0.01% to about 2%, cerium in an amount in a range of about 0% to about 0.05%, lanthanum in an amount in a range of about 0% to about 0.05%, calcium in an amount in a range of about 0.1% to about 0.1%, silicon in an amount in a range of about 0% to about 1%, nickel in an amount in a range of about 0.01% to about 5%, and/or a balance comprising iron, wherein phosphorus, if present, is in an amount less than about 0.0075% and/or sulfur, if present, is in an amount less than about 0.01%.

Steel of the present invention may be in any suitable form. In some embodiments, the steel is in the form of a plate having a thickness in a range of about 6 mm to about 100 mm. In some embodiments, the steel is in the form of a plate having a thickness of about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 mm. In some embodiments, the steel is in the form of a plate having a thickness of about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 inches or more. In some embodiments, the steel is in a cast or wrought form. In some embodiments, the steel is in the form of a wrought plate, which may have a thickness of 1 inch or greater (e.g., up to 5 or 10 inches).

Steel of the present invention may have a yield strength, tensile strength, minimum tensile ductility, Brinell Hardness (BHN), and/or impact toughness as described herein.

In some embodiments, the steel may have a yield strength of about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, or 1500 MPa, as measured in accordance with ASTM E8/E8M (ASTM E8/E18M-16a, Standard Test Methods for Tension Testing of Metallic Materials, ASTM International, West Conshohocken, Pa., 2016). In some embodiments, the steel has a yield strength of greater than 1000 MPa.

The steel may have a tensile strength of about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, or 2000 MPa, as measured in accordance with ASTM E8/E8M.

The steel may have a minimum tensile ductility in a range of about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 70%, as measured in accordance with ASTM E8/E8SM.

The steel may have a BHN of about 300, 310, 320, 330, 340, or 350.

The steel may have an impact toughness of about 30, 40, 50, 60, 70 80, 90, 100, 110, or 120 feet per pound at −40° C., as measured in accordance with ASTM E23 (ASTM E23-16b, Standard Test Methods for Notched Bar Impact Testing of Metallic Materials, ASTM International, West Conshohocken, Pa., 2016).

In some embodiments, a steel of the present invention has a minimum yield strength of 500 MPa and a minimum tensile ductility of 30%, or a minimum yield strength of 1,000 MPa and a minimum tensile ductility of 10%. In some embodiments, a steel of the present invention has the same or equivalent strength requirements as quenched and tempered steels with hardness requirements between 300 and 350 BHN. A steel of the present invention may have the same or equivalent properties as low carbon steels. In some embodiments, a steel of the present invention may be a direct substitute for a carbon steel (e.g., a low carbon steel) at the same geometries. A steel of the present invention may exhibit high-energy absorption and/or a ductility greater than 30% at 1000 s⁻¹.

In some embodiments, steel of the present invention has a density less than the density of a steel of standard chemistry. For example, steel of the present invention may have a density of less than 7.8 g/cm³. In some embodiments, steel of the present invention has a density of less than about 7 grams per cubic centimeter (g/cc). In some embodiments, steel of the present invention has a density of 6.7 g/cc or less. In some embodiments, the steel has a density in a range of about 6.5 to about 7 or 7.2 g/cm³.

A steel of the present invention may have a reduced density as compared to a conventional carbon steel, a conventional Fe—Mn—A—C steel (e.g., Fe-13Mn-10Al-1C or Fe-30Mn-9Al-1Si-0.9C-0.5Mo), and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention. In some embodiments, the steel has a density that is at least about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% less than a conventional carbon steel, a conventional Fe—Mn—Al—C steel, and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention. In some embodiments, a steel of the present invention has a reduced density (e.g., about 10% less) compared to a conventional carbon steel and has the same or equivalent mechanical properties as the conventional carbon steel.

Steel of the present invention may comprise an austenite matrix. In some embodiments, the steel comprises a primary austenite matrix. A “primary austenite matrix” as used herein refers to an austenite matrix that is present in the steel in a volume fraction amount of at least 50%. The volume fraction of the austenite matrix in the steel may be in a range of about 80% or 90% to about 100%. In some embodiments, the austenite matrix comprises ferrite (e.g., ordered ferrite), kappa carbide, and/or vanadium carbide, each of which may be uniformly dispersed throughout the austenite matrix. In some embodiments, a steel of the present invention has a microstructure comprising austenite, dispersed ordered ferrite, and evenly distributed carbides. Ferrite (e.g., ordered ferrite) may be present in a volume fraction of less than 10%, kappa carbide may be present in a volume fraction in a range of about 0.1% to about 15%, and/or vanadium carbide may be present in a volume fraction of less than 1%. In some embodiments, interdendritic regions may be formed of ordered ferrite with a kappa carbide structure precipitated throughout the matrix. In some embodiments, vanadium carbides may provide grain refinement.

In some embodiments, the steel comprises a microstructure having an average grain size of about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 microns. In some embodiments, the steel comprises an austenite matrix having an average grain size of about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 microns.

Steel of the present invention may be substantially non-magnetic, which may be determined by measuring the magnetic permeability of the steel in accordance with ASTM A342/A342M (ASTM A342/A342M-14, Standard Test Methods for Permeability of Weakly Magnetic Materials, ASTM international, West Conshohocken, Pa., 2014). In some embodiments, the relative magnetic permeability (μ_(r)) may be as low as 1.005.

In some embodiments, a steel of the present invention may have reduced or no cracks compared to a different Fe—Mn—Al—C steel (e.g., a conventional Fe—Mn—Al—C steel and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention). In some embodiments, a steel of the present invention may have no cracks that are visible to the human eye. Cracks, if present in the steel, may only be visible with the aid of a microscope. Oxide scale may be present on a surface of steel of the present invention. When present, oxide scale may be less than 500 microns from a surface of the steel and/or may not penetrate into the steel. In some embodiments, the oxide scale has a thickness of less than 500 microns.

In some embodiments, a steel of the present invention may have reduced weight compared to a conventional carbon steel (e.g., a low carbon steel), a conventional Fe—Mn—Al—C steel, and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention. For example, a steel of the present invention may have a weight that is at least about 5% or 10% less than a conventional carbon steel (e.g., a low carbon steel), a conventional Fe—Mn—Al—C steel, and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention. In some embodiments, a steel of the present invention has a weight that is reduced by about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or more compared to a conventional carbon steel (e.g., a low carbon steel), a conventional Fe—Mn—Al—C steel and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention.

A steel of the present invention may be in a form for Rolled Homogeneous Armor (RHA) and/or suitable as an alternative steel alloy for RHA. A steel of the present invention may meet the requirements for and/or be classified as a Class V RHA Grade under MIL-A-12560. The steel may be a wrought plate having a thickness of 1 inch or greater, such as, for example about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 inches or more. In some embodiments, the steel is a ballistically capable material. “Ballistically capable” as used herein, refers to a material that can be used to mitigate, stop, and/or impede (partially or completely) a kinetic energy penetrator. In some embodiments, a steel of the present invention (e.g., steel plate) partially or completely stops a kinetic energy penetrator from penetrating through the steel.

In some embodiments, a steel of the present invention may have a mass efficiency of greater than 1 or 1.1. In some embodiments, a steel of the present invention may have a mass efficiency in a range of 1 to 1.2.

In some embodiments, the steel and/or steel plate of the present invention may be used for and/or suitable for dynamic impact applications, such as, e.g., where high specific strength is required to minimize structural weight burden of large automotive ground systems. Heavy ground systems cannot be fabricated from automotive sheet and thus require thicker materials with different considerations in order to support structural loads. However, because of the increased mass requirements, additional structural weight unnecessarily burdens vehicle systems making the overall system less efficient. In some embodiments, a steel and/or steel plate of the present invention may reduce these burdens and/or allow for additional capability for ground systems. A ground system may include a steel and/or steel plate as described herein. Example ground systems include, but are not limited to, tanks, armored vehicles, armored personnel carriers, armored combat support vehicles, mine-protected vehicles, and manned or unmanned armored fighting vehicles. In some embodiments, a steel and/or steel plate of the present invention may be directly substituted for existing materials, which may prevent or avoid design rework and/or may provide a reduction in weight of the ground system (e.g., as compared to a conventional steel used in a ground system, a conventional Fe—Mn—Al—C steel, and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention).

In some embodiments, a steel of the present invention is a lightweight structural steel with age hardenable tunability that may have comparable or improved hardness, ductility, strength, and/or toughness as compared to a conventional carbon steel, a conventional Fe—Mn—Al—C steel, and/or a Fe—Mn—Al—C steel not in accordance with a composition and/or method of the present invention.

According to some embodiments of the present invention, provided is a method of manufacturing a steel plate. A method of the present invention may prepare and/or provide a steel of the present invention in the form of a steel plate. In some embodiments, a method of the present invention comprises casting an alloy to form a preform; heating the preform to a temperature in a range of about 1000° C. to about 1200° C.; and rolling the preform to form a steel plate. The preform may be an ingot or a slab. In some embodiments, the method comprises a reflect ingot cast or continuous casting step.

The alloy may have any suitable composition. In some embodiments, the alloy has a composition as described herein for a steel of the present invention. In some embodiments, the alloy comprises, by weight percent, a balance comprising iron, manganese in an amount in a range of about 15% to about 35%, aluminum in an amount in a range of about 7 to about 12%, carbon in an amount in a range of about 0.7% to about 1.1%, molybdenum in an amount in a range of about 0.5% to about 1.5%, vanadium and/or niobium in an amount in a range of about 0.01% to about 2%, calcium in an amount in a range of about 0.01% to about 0.1%, and/or silicon in an amount in a range of about 0.01% to about 1.5%. The alloy may comprise phosphorus in an amount of less than about 0.0075%, sulfur in an amount of less than about 0.01%, and/or nitrogen in an amount of less than about 0.01%. The alloy may be handled in the method in such a manner so as to minimize edge and/or surface cracking during hot working operations.

A method of the present invention may utilize a material and/or alloy that is low in one or more impurities, such as, e.g., phosphorus, sulfur, and/or nitrogen. In some embodiments, a method of the present invention takes measures to guard against alloy and/or melt stock impurity contamination, such as, e.g., phosphorous contamination. In some embodiments, an alloy may comprise a high purity electrolytic iron and/or electrolytic manganese. In some embodiments, a method of the present invention may comprise calcium treating (e.g., heavy calcium treating) the alloy with argon stirring, which may aid in removing phosphorus. A method of the present invention may further comprise adding a misch metal (e.g., in an amount less than about 1% by weight of the alloy), which may aid in minimizing the amount of phosphorous in the alloy and/or steel plate. An example misch metal may contain varying amounts of cerium, lanthanunm, neodymium, and praseodymium.

In some embodiments, heating of the preform may comprise heating the preform to a temperature of about 1000° C., 1050° C., 1100° C., 1150° C., or 1200° C. The temperature of the preform may be monitored before, after, and/or during the heating step using methods and/or devices known to those of skill in the art, such as, e.g., using a pyrometer.

The preform and/or steel plate may have a temperature of 900° C. or more during and/or after rolling the preform to form the steel plate. In some embodiments, at the conclusion of rolling the preform to form the steel plate, the temperature of the steel plate is 900° C. or more. In some embodiments, rolling of the preform to form the steel plate comprises hot rolling the preform and maintaining the preform and/or steel plate at a temperature of at least 900° C., Alternatively or in addition, the rolling step may comprise adiabatic heating of the preform and/or steel plate. In some embodiments, no external heating is used and/or provided during the rolling step.

Rolling of the preform to form the steel plate may comprise rolling the preform with one or more roll passes. A roll pass may provide a reduction in thickness of the preform of about 10% or less. In some embodiments, the rolling step provides a reduction in thickness of the preform of about 15 mm or more per pass (e.g., about 15, 20, 25, 30, or 35 mm or more). In some embodiments, the rolling step provides a reduction in thickness of the preform of about 15 mm to about 35 mm.

A method of the present invention may further comprise solution treating, performing a quench (e.g., a water quench), and/or aging the steel plate. Solution treating of the steel plate may be conducted in an open air furnace, vacuum, and/or an environmentally controlled furnace. In some embodiments, a water, oil, salt, and/or gas quench is performed. In some embodiments, after solution treatment, the steel plate may be immediately removed from the solution, treatment environment and placed in a quench medium as quickly as possible to provide a rapid quench and cooling to room temperature. As one skilled in the art will recognize, the water, oil or salt are separate baths into which the solution treated steel plate may be placed. A gas quench is typically done in an integrated system, such as, e.g., a vacuum or environmentally controlled atmosphere, into which the solution treated steel plate is placed.

In some embodiments, a method of the present invention comprises solution treating the steel plate at a temperature in a range of about 900° C. to about 1200° C. (e.g., about 1000° C.) to provide a solution treated plate; performing a quench (e.g., a water quench) on the solution treated plate to provide a quenched plate; and aging the quenched plate. Aging the quenched plate may comprise exposing the quenched plate to a temperature in a range of about 450° C. to about 600° C. (e.g., about 530° C.), optionally for up to about 15 hours (e.g., about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 hours). In some embodiments, aging may be carried out for a period of time to attain a desired hardness.

In some embodiments, a method of the present invention comprises solution treating the steel plate at a temperature in a range of about 900° C. to about 1200° C. (e.g., about 1000° C.) to provide a solution treated plate; performing a quench (e.g., a water quench) on the solution treated plate to provide a quenched plate; exposing the quenched plate to a temperature in a range of about 400° C. to about 500° C. for a period of time (e.g., about 1 or 2 hours to about 3 or 4 hours); and exposing the quenched plate to a temperature in a range of about 600° C. to about 650° C. for a time period (e.g., about 1 or 2 hours to about 3 or 4 hours). The quenched plate may be exposed first to a temperature in a range of about 400° C. to about 500° C. and then to a temperature in a range of about 600° C. to about 650° C.

In some embodiments, a method of the present invention comprises minimizing or removing a decarborized surface layer of the preform and/or steel plate. Any suitable method to remove or minimize the decarburized layer may be used in a method of the present invention. In some embodiments, when the method comprises an open air heat treatment (e.g., at a temperature of 1000° C. or more), removal of a decarburization layer is performed. In some embodiments, a coating on one or more surfaces of the preform and/or steel plate may be provided to prevent decarbonization. In some embodiments, the alloy is provided with a carbon content in an amount suitable to provide the desired final carbon content even if decarbonization were to occur during the method of forming the steel plate.

In some embodiments, a forging step may be performed, such as, but not limited to, when the preform (e.g., an ingot) is porous. The forging step may be provided in the method after heating the preform to the temperature in a range of about 1000° C. to about 1200° C. and prior to rolling the preform to form the steel plate. In some embodiments, the preform is forged to a given or predetermined thickness to form a forged preform. The thickness of the forged preform may be in a range of about 8 to about 14 inches. The method may further comprise performing a surface treatment, such as, but not limited to, surface grinding the forged preform, and/or the method may further comprise coating the forged preform. In some embodiments, the forged preform is heated to a temperature in a range of about 1000° C. to about 12000° C., and rolling may be subsequently performed on the forged preform to form the steel plate. As described above, in some embodiments, rolling may be carried out such that each roll pass may provide a reduction in thickness of the forged preform of about 10% or less and/or provide a reduction in thickness of the forged preform of about 15 mm or more per pass.

In some embodiments, a method of the present invention comprises grain refinement during ingot processing and/or hot rolling operations. In some embodiments, a method of the present invention may cause the austenite matrix to spinodally decompose, which may result in an increase in the matrix hardness. A method of the present invention may provide a microstructure as described herein that allows for a stable matrix that supports a large content of aluminum in a primary iron matrix, which may provide for a reduced density of the steel and/or increased strength of the resulting product (e.g., a heat treated steel plate).

A steel of the present invention may be obtained using and/or a method of present invention may utilize existing manufacturing equipment and/or process techniques known to those of skill in the art without the need for specialized equipment, which may thereby minimize the cost in manufacturing the steel and/or steel plate. A method of the present invention may utilize existing steel making equipment, optionally with slight modifications to standard melt practices.

A method of the present invention may manufacture or prepare a steel of the present invention using an open air induction furnace and/or vacuum furnace. In an open air furnace or vacuum furnace, the oxygen content may be, e.g., less than 6 ppm. For open air induction melting furnaces, MgO refractory linings may be utilized. Alumina and silica refractory may not be used in a method of the present invention since they may exchange oxygen with the liquid steel, which may degrade furnace linings and/or increase inclusion content in the steel. In some embodiments, a cover gas or a synthetic slag to protect the melt form atmospheric oxidation is not necessary. Olivine sand based molds or preheated investment shell molds may be used for casting mold material. In some embodiments, where melting is performed utilizing an open air furnace, a cover gas (e.g., argon) may be used, which may minimize atmosphere reactivity.

A method of the present invention may minimize (e.g., may not total more than 5% of volume fraction) one or more of the following: carbide precipitation as an upper transformation product, the formation of a weak outer columnar grain structure, and the formation of a weak, incohesive outer grain boundary structure with embrittled grain boundaries. In some embodiments, such structures are present in a volume fraction total amount of less than 5%. In some embodiments, a method and/or composition of the present invention may overcome the phase formation and weak grain boundary phenomenon with respect to preventing crack formation and/or crack growth in order to efficiently produce a high Al containing Mn steel alloy. In some embodiments, one or more steps in a method of the present invention (e.g., preform coating for preheat in a non-atmosphere controlled environment and/or sequenced hot work processes) may strengthen otherwise weak columnar exterior ingot grain boundaries, which may resolve crack formation on the surface of the preform and/or steel.

Methods of cutting, machining, and/or processing steel known to those of skill in the art may be used in a method of the present invention. In some embodiments, a blunt carbide and/or aluminum oxide cutting tool is used for machining operations. To prevent tool wear and/or machine tool damage, slow speeds and/or feeds may be used. In some embodiments, a steel of the present invention may be flame, abrasive, and/or band saw cut. The saw blade may be carbide tipped. Flame cutting may be done with a powder injection.

The present invention is explained in greater detail in the following non-limiting examples.

EXAMPLES Example 1

An industrial heat of 45 tons of the Fe-28Mn-8Al-1Si-0.9C-0.55Mo-0.55V nominal chemistry was produced. This heat was produced using an electric are furnace. As with foundry and lab furnace techniques, electrolytic Mn was used to minimize P. The ingots were prepared for rolling by grinding to remove the oxidized and decarburized layer, painted with an oxidation barrier, heated to 1150° C., and roiled to a final thickness of 1″ thick plate. The plate was subsequently reheated to 1050° C., water quenched, and aged for 10 hours at 530° C. The mill that produced the lab measured phosphorous at 0.003 wt. %.

The 1″ thick plate was tested against the MIL-DTL-12560-K. Class I Rolled Homogenous Armor (RHA) specification utilizing .50 caliber APM2 projectile. The plate successfully met the acceptance criteria for Class I RHA as shown in FIGS. 1-4. FIG. 1 is an image of the strike face of the steel plate during ballistic testing and shows the entrance penetration using .50 caliber APM2 test munition. The test was used for comparative data analysis to Rolled Homogeneous Armor. FIG. 2 is at image of the back face of the steel plate during ballistic testing and shows both complete and partial penetration using .50 caliber APM2 test munition. FIG. 3 is an image of the strike face of the steel plate during ballistic testing and shows the entrance penetration using 20 mm fragmentation simulation projectile (FSP) test munition. The test was used for comparative data analysis to Rolled Homogeneous Armor, FIG. 4 is an image of the back face of the steel plate during ballistic testing and shows both complete and partial penetration using 20 mm FSP test munition.

The foregoing is illustrative of the present invention, and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein. All publications, patent applications, patents, patent publications, and other references cited herein are incorporated by reference in their entireties for the teachings relevant to the sentence and/or paragraph in which the reference is presented. 

1. A steel comprising, by weight percent: manganese in an amount of about 15% to about 35%, aluminum in an amount of about 7% to about 12%, carbon in an amount of about 0.7% to about 1.1%, molybdenum in an amount of about 0.5% to about 1.5%, vanadium or niobium in an amount of about 0.01% to about 2%, calcium in an amount of about 0.01% to about 0.1%, silicon in an amount of about 0.01% to about 1.5%, and a balance comprising iron.
 2. The steel of claim 1, further comprising, by weight percent, at least one of: cerium in an amount up to about 0.05%, lanthanum in an amount up to about 0.05%, nickel in an amount up to about 5%, chromium in an amount up to about 5%, cobalt in an amount up to about 5%, and tungsten in an amount up to about 5%.
 3. The steel of claim 1, wherein the steel comprises vanadium in an amount of about 0.01% to about 2%.
 4. The steel of claim 1, wherein manganese is present in an amount of about 28% to about 35%.
 5. (canceled)
 6. The steel of claim 1, further comprising one or more impurities, wherein the one or more impurities comprise, by weight percent, phosphorus in an amount of less than about 0.0075%, nitrogen in an amount of less than about 0.01%, and/or sulfur in an amount of less than about 0.01%.
 7. (canceled)
 8. The steel of claim 1, wherein the steel is in the form of a plate having a thickness of 1 inch to about 5 inches.
 9. The steel of claim 1, wherein the steel has a yield strength of about 500 or 1000 MPa to about 1500 MPa, as measured in accordance with ASTM E8/E8M.
 10. The steel of claim 1, wherein the steel has a tensile strength of about 800 or 1000 MPa to about 2000 MPa, as measured in accordance with ASTM E8/E8M.
 11. The steel of claim 1, wherein the steel has a minimum tensile ductility of about 10% or 30% to about 60%, as measured in accordance with ASTM E8/E8M.
 12. The steel of claim 1, wherein the steel has a density of less than about 7 grams per cubic centimeter (g/cc).
 13. The steel of claim 1, wherein the steel comprises an austenite matrix, optionally wherein the steel comprises a primary austenite matrix.
 14. (canceled)
 15. The steel of claim 13, wherein the austenite matrix comprises ferrite (e.g., ordered ferrite), kappa carbide, and/or vanadium carbide. 16.-17. (canceled)
 18. The steel of claim 1, wherein the steel has a Brinell Hardness (BHN) in a range of about 300 to about
 350. 19.-20. (canceled)
 21. The steel of claim 1, wherein the steel comprises a microstructure having an average grain size in a range of about 10 or 30 microns to about 100 microns.
 22. The steel of claim 1, wherein the steel has an impact toughness of about 30 feet per pound at −40° C. to about 120 feet per pound at −40° C., as measured in accordance with ASTM E23.
 23. (canceled)
 24. The steel of claim 1, wherein oxide scale is present on a surface of the steel and the oxide scale is less than 500 microns from a surface of the steel.
 25. A process for manufacturing a steel plate comprising: casting an alloy to form a preform, the alloy comprising, by weight percent, manganese in an amount of about 15% to about 35%, aluminum in an amount of about 7 to about 12%, carbon in an amount of about 0.7% to about 1.1%, molybdenum in an amount of about 0.5% to about 1.5%, vanadium or niobium in an amount of about 0.01% to about 2%, calcium in an amount of about 0.01% to about 0.1%, silicon in an amount of about 0.0% to about 1.5%, and a balance comprising iron; heating the preform to a temperature in a range of about 1000° C. to about 1200° C.; and rolling the preform to form a steel plate.
 26. The method of claim 25, wherein the preform has a temperature of 900° C. or more during and/or after rolling the preform to form the steel plate. 27.-29. (canceled)
 30. The method of claim 25, further comprising: solution treating the steel plate at a temperature of about 1000° C. to provide a solution treated plate; performing a quench (e.g., a water quench) on the solution treated plate to provide a quenched plate; and aging the quenched plate.
 31. (canceled)
 32. The method of claim 25, further comprising: solution treating the steel plate at a temperature of about 1000° C. to provide a solution treated plate; performing a quench (e.g., a water quench) on the solution treated plate to provide a quenched plate; exposing the quenched plate to a temperature in a range of about 400° C. to about 500° C. for a time period of about 2 hours to about 3 hours; and exposing the quenched plate to a temperature in a range of about 600° C. to about 650° C. for a time period of about 2 hours to about 3 hours.
 33. The method of claim 25, further comprising carburizing the preform and/or steel plate.
 34. The method of claim 25, further comprising, after heating the preform to the temperature in a range of about 1000° C. to about 1200° C. and prior to rolling the preform to form the steel plate, forging the preform to a given thickness to form a forged preform, optionally performing a surface treatment and/or coating on the forged preform, and heating the forged preform to a temperature in a range of about 1000° C. to about 1200° C.; and wherein rolling the preform to form the steel plate comprises rolling the forged preform to form the steel plate. 35.-38. (canceled) 